In the nuclear analysis field including positron lifetime spectrometers and positron angle-momentum association analyzers, in the nuclear detection field including double-compliance energetic particle discriminators and in the medical imaging field including the Positron Emission Tomography (abbreviated as PET hereinafter), a main working principle of detecting energetic particles is to convert a high-energy ray into an electric signal and then obtain various information of a particle event with a method of the fast electronics. In some applications of meters involving coincidence logical operations and time stamps, shaping a scintillation pulse, which slows down the process, may affect a time performance of the scintillation pulse and may increase a probability of stacking event pulses. In this case, it is more desirable to directly digitize the scintillation pulse.
In a complete digitization of a scintillation pulse, an Analog to Digital Converter (abbreviated as ADC hereinafter) with a high bandwidth and a high sampling rate is adopted to directly sample and quantize the scintillation pulse. Such digitization method cannot meet an actual requirement of multi-channel systems due to a high cost. And the above digitization solution may be simplified in two manners to reduce the cost. In one manner, the sampling rate is reduced. In this case, due to a low sampling frequency, a high-frequency component of a non-shaped scintillation pulse signal not only cannot be sampled, but also affects accuracy of a component around a Nyquist frequency due to aliasing in the frequency domain. In order to alleviate the above defect, a shaping process is added between a process of outputting the scintillation pulse and a process of digitizing the scintillation pulse. In the shaping process, a component of the scintillation pulse having a frequency higher than the Nyquist frequency is attenuated and a low-frequency component of the scintillation pulse is reserved, to reduce the aliasing in frequencies due to the digitizing of the scintillation pulse. However, it is impossible to sample a component having a frequency higher than the Nyquist frequency due to a limitation by the Nyquist frequency itself.
Besides the manner in which the ADC is simplified in the time axis, in another manner, the ADC is simplified in the voltage axis. An effective bandwidth of the ADC simplified in the voltage axis may be improved by using an open-loop designation, which is favorable to a high-speed signal processing. For example, a digitization method involving several comparators/ADC units and an ADC with interleaving open-circuit time all perform in this manner. Such ADC is characterized by a high sampling rate and a high bandwidth but a limited quantization accuracy. Since the scintillation pulse has distinctive priori knowledge, with which the accuracy of recovering a digitalized signal may be improved and a quantization level may be set optimally.
Therefore, for the above sparse quantization level ADC, it is desired to provide a new method and a new system for recovering scintillation pulse information to address issues existing in the conventional technology.